Radio receiving system



June 10, 1930. s. E. ANDERSON RADIO RECEIVING SYSTEM Filed Aug. 20, 1925 imam/an 67am? 54/119930 l-Il'lI'I-lI-llll ll;

To secure a hig and good quality reproduction of thesignals,

Patented June 10,1930 7' mmSims:

SIDNEY n. Aivnmzson,onmAriinwoong iinwJnnsnY, ASSIGNOR' rownSTnniv v PATE T Bic E TRICIGOMPANY," iiiconroRATnn, A oon-rone rioiton NEW 2on1:

RADIO RECEIVING svsriiia Application filed August 20,1925; 'seriai'ixiq. 51,391. i l

' is combined .With local oscillations to produce an intermediate frequency. wave. modulatedin accordance with signals, the intermediate 10 frequency Wave bein'giamp'lified and then'detected to yield'the signals. In one class of systems of this typea separate oscillator is used to supply oscillations of a frequency different from that of the received wave to a mediatefrequency Wave. 7 4

' At the present time it is the general practice to employ aspace discharge device havingintercoupled input and output. circuits,

includinga tuned circuit for determining the frequency of the oscillations generated, as a source for producing thedocally supplied oscillations. The local source is coupledto 5 the detectorin such manner, as by a. loose inductive coupling, that the tuned receiving circuit; and the frequency determining circuit of the source may be adjusted independently of each other.

' h degreerof amplification tandem circuits have been employed tofi-ainplify the intermediate frequency Wave. Hoivever, owing to the'tendency to produce oscillations of undesired frequencies or singing:

in the individual amplifier circuits and 1n the system includin'g'the tandem connected circuits, it has been the practice either ;to limit the amplification effected in each ciia 40 cuit to a low value, or to provide each circuit and the system'with' anti-singing arrangements- Systemsemploying the first mode of procedure to efiect a high degre'eof aniplification require a large number oftandem 1 connected circuits and those employing anti sin in devices are exceptionally COIIlph- 7 l I h V I Foracomplete understan'dmgof the-mven tio'n referenceshould be made to the following specification read 'in 'conjunction with the I; 1'00" cated, I V The present invention provides a s inplear- 'rangement adapted to overcome the disadvantages referred to above.

detector in which the oscillations and incorn-- ing Wave are combined tO PI'Odl1CBl1l'l&1Ilt6I-4 devices adapted to 'qii'encies. V

Iii-accordance with this'invention the detec tor is provided With a high resistance leak path through which the local oscillations are supplied to the detector, and tandem coni nected circuits, each'selective of the- Wave to be repeated and including.athree-electrode space discharge device, have dissimilar eleced by a pathincluding a condenser of low impedance for: certain of the frequency coinv 'ponents to be amplified, so that a frequency trodes of certain of said devices interconnectband of appreciable Width may be amplified to a high degreeby a limited number of-tandem connect-ed.- lamplifier circuits ivithout causing'distortion of the repeated Wave, With d the result that good quality reproduction of. 1

thesignalsinay be accomplished.

The preceding statement, describing ina general'Way one arrangement embodying the: 1I1Vel1t1011, 1S;glVQIl;m8I'Qly for the; purpose of briefly disclosing. its-nature and is not in-* tended to indicate the, scope of the invention, o 1 The novel features and-combinations which are believed to be characteristic of this invention will, be pointed out with, particularity in.;- I

the subjoined claims,

of oscillations including a tuned frequency determining circuit, to'be coupled'to a detector in such manner that there Will be no interaction between the selective and frequency One object of this invention is to permit. a selective receiving-circuit and a, local source tandem connected circuits selective of the fre Still another object is to selectively effect.

quen cy-band and includingelectric discli aigej, f amplify the bandoffreg ahigh degree of amplification'of a relatively:

Wide bandof frequencies Without causing distortion, whereby the different frequency com-- ponents of the band maybe faithfully 'peated. i

' attached drawingjinwhich the single figure illustrates a radio telephone receiver embodying the invention.

; Referring to the drawing, there is shown an antenna 1 connected through a variable inductance coil 2 to ground. Coupled to the antenna is a receiving circuit comprising a coil Sinductively associated with coil 2, an adjustable coil 4 and a variable condenser 5.

The coils 3 and 4 and condenser 5 cooperate to'constitute'a tuned receiving circuit selective of the incoming wave. The coupling between the antenna circuit and the second- 1 ary circuit may be varied by adjusting the coil 2. The tuning of the secondary circuit may be varied to select different frequency waves by adjusting condenser 5 or the coupling bet-ween coil 3 and coil 4 or both.

An incoming wave incident upon the antenna is impressed upon the input circuit of detector 6' through the receiving circuit 3--4'5. Local oscillations of the desired frequency will also be supplied from source '7 to the input circuit of the detector 6.

The source 7 is herein shown by way of example as comprising a space discharge device 8 having its input and output circuits intercoupled in the well known manner to generate oscillations, the frequency'of which is determined by a tuned circuit comprising coils 10, 10A and condenser 11. The frequency of the oscillations generated may be controlled by adjusting condenser 11 or the I coupling between coils '10 and 10-A. Coil .second path through which energy is supplied to it from the antenna and secondary circuits. This path extends from the grid of tube 6, tuned circuit 345 to the cathode of 6 and the space path between its cathode and grld.

The resistance 9 in addition to operating as a leak path for the detector 6 also serves as a coupling through which oscillations are supplied from the source 7 to the input electrodes of the detector. By virtue of this mode of coupling theoscillator and detector, the tuning of the selective receiving circuit 3+5 and that ofthe frequency determining circuit 1011 of the oscillator are rendered substantially independent of each other. In other words, the tuned receiving circuit 345 may be adjusted to select the incoming wave without reacting upon the fre- .quency wave.

quency determining circuit 10-11 of the oscillator and vice versa.

Let it be assumed that the incoming wave comprises a carrier current modulated by speech, that the unmodulated component and the modulation products, i. e. both side bands. are received, and that speech constitutes a frequency band of 2500 cycles. The received wave will, therefore, have a band Width of approximately 5000 cycles.

As thus far described, the system operates as follows: Having adjusted the circuit 3el5 to select the incoming wave and frequency determining circuit 10-11 of source 7 to supply oscillations of corresponding fre quencydiffering from the incoming wave, there will be produced in the output circuit of the detector waves modulated by speech, which corresponds to the sum and to the difference of the received frequency and the frequency of the local oscillations. As is usual in successive detection systems, especially for short wave transmission, the differ ence frequency is selected and amplified by the intermediate amplifier comprising three tandem connected circuits each selective of the difference frequency and including one of the space discharge devices 13, 1d and 15, respectively.

The unmodulated component of the intermediate frequency wave will be assumed to be of the order of 50,000 cycles,hencethe total frequency band supplied to the intermediate frequency amplifier will extend from 7,500 cycles to 52,500 cycles, i. e. will comprise a frequency band of 5,000 cycles.

Secondary windings of the coupling transformers 16l7--18 are designed to each cooperate with the inherent reactances of the circuits, including the internal capacity between the electrodes, of the tubes 18'14-15, respectively, to select the intermediate fre- The voltage of the intermediate frequency wave impressed upon the input electrodes of the amplifier 13 may be controlled by the potentiometer 19 connected in parallel with the secondary Winding of the transformer 16.

The amplified intermediate frequency wave is supplied through the couplingtransformer 20 to the device 21, herein shown as a three electrode space discharge device, in which it is detected to yield speech currents. These currents are impressed upon the device 23 through the transformer 22 and after being amplified by the device 23 are supplied to the receiver 24. A by-pass condenser 25 is connected across the primary of transformer 22 in order to afford a low impedance path for any intermediatefrequency carrier present in the output circuit of detector 21.

In the operation of the system described above, it was found that when the intermediate frequency amplifier was adjusted to effect the desired amplification, namely, of

occurred in this portion of the system. Even though oscillations did not occur, the regenoration or tendency toward oscillation served undesired frequencies or singing sometimes toa'ccentuate certain components lying within the intermediate frequency band. This resulted in the transmissioncharacteristic of the amplifier being very irregular and the signals reproduced by the receiver 24- were of exceptionally low quality, and in some cases almost unintelligible. V It appears probable that the inherent reactances of the amplified circuit, including the inter-electrode capacities of the tubes and inductive and capacity effects of the interstage transformers and connecting leads, co.- operate to produce resonant paths for certain frequency components lying within the band, these resonant paths being either in the cir 'cuits individual to each amplifying device or in the intercoupled circuits com prising the complete amplifier. Under these conditions the components selected by the resonant paths were amplified to a greater extent than the other components, with the result that regeneration or oscillations occurred at the selectedgfrequencies.

o In order to overcome the above noted disadvantages, the plate of the first amplifier 13 was connected to the grid'electro-de of the third amplifier 15 by a path including a condenser 26 of small capacity.

lVhen a condenser 26 of theproper capacity is employed, it has beenfound that the trans-. mission characteristic of the amplifier was substantially uniform over the frequency range of the band being amplified. Further, it was found that if the capacity of this'condenser was increase-d beyond the proper value to prevent singing in thecircuit, it resultedmerely in a reduction of the amplification eftected. It will, therefore, be apparent that the actual value of this condenser. is not very critical and'hence that. a capacity of fixed value requiring no adjustment, as is the case supplying to said amplifier a wave extending over a relatively wide frequency 'band, and' means for preventing distortion of saidwave,

said last mentioned means'comprising. a ca-' pacity element connecting the plate of one discharge device to the grid of a following discharge device other than the next succeeding device. 3. An amplifier comprising a plurality of tandem connectedcircuits eachselective of a wave to be amplified, a space discharge device having a cathode, an anode anda grid included in .eachof said circuits, means for over a relatively wide frequency'band, and means,-connecting,the anode of one of said discharge devices'to the grid of a following discharge device other than the next succeeding'one, for preventing distortion of the am-' plifie d Wave. v

4:, An amplifier comprising a plurality'of tandemiconnected circuits each including a space discharge device having a cathode, an anode and a grid,'inductive means for con-- necting said circuits in tandem and forcooperating with the inherent capacity'between selective circuits, means for supplying to said amplifier a wave extending over a relatively v wide frequency band, and means for preventing'regeneration and distortion of the amsupplying to said amplifier a wave extending the electrodesof said devices toconstitute plified wave band, said last mentioned means comprlsing a reactance element for connecting aplate electrode of-one discharge device with a grid electrode of another discharge de- "vice other than the adjacent discharge device. In witness whereof, I hereunto subscribe my n'amethis 14th day of August, A. D., 1925.

SIDNEY E. ANDERSON.

' with the usual stabilizer, may be applied'to I the system. J

What is claimed is: V

1; An amplifier comprising a plurality of tandem connected circuits selective of a wave to be amplified each circult mcluding a threeelectrode space discharge device, means for supplying to sald amplifier a waveextendlng over a relatively widefrequency band, and

means for preventing regenerative operation of said amplifier, said last mentioned means comprising a capacity element connecting anoutput electrode of one device Withan input electrode of another device other than the adjacent device.

2. An amplifier comprising a plurality of flee 

